A method is known, in the state of the art, for the in-line detection of surface defects present on bars or wire during rolling, drawing or extrusion operations, or at the end of them. This known method provides to use electromagnetic device's that are disposed downstream of the rolling line, or downstream of a relative rolling unit and which, by means of coils able to generate an electromagnetic field and relative reception coils, detect the presence of surface defects, such as cracks, inclusions, microfissures.
Detection devices of the electromagnetic type as above cited are disclosed in the French applications FR-A-2.131.872, FR-2.686.699 and FR-A-2.426.257, in the European patent application EP-A-0.995.507 and in the Japanese patent application JP-A-61.118.654.
In general, in methods based on the use of coils, in order to obtain highly sensitive detection of the defects, the so-called filling factor plays an important role. The filling factor is the ratio between the area of the central hole of the coils through which the rolled product passes, and the area of the cross section of the rolled product. The higher the filling factor, the more sensitive the device. On the other hand, when the filling factor is high, the risks of contact of the rolled product increase, in particular if it is subject to vibrations and transverse movements with respect to its axis, against the internal wall of the hole of the coils, with consequent possible damage and loss of sensitivity of detection.
One disadvantage of this known method is that, since detection of this type is sensitive to the transverse movements of the rolled product, it is not possible to guarantee precise results due to the vibrations to which the rolled product is subject when it is no longer guided inside the relative rolling unit and due to the fact that, for this reason too, the filling factor cannot have a high value, near to the unit, due to the risks of contact mentioned above.
This low sensitivity leads to medium to small surface detects being overlooked, for example those less than 2% of the diameter of the rolled product, because they are not accurately detected.
Another disadvantage of known detection devices is that they require purpose-made installation structures, which must be re-equipped and prepared every time the rolling units are reconfigured for a new format of the rolled product being worked.
Another known detection device, suffering of the above mentioned disadvantages, is disclosed in the French application FR-A-2.674.459, wherein an inspection group, provided with detection electromagnetic coils of the type as above discussed, is interposed between two guide elements, an upstream guide element and a downstream guide element. This is a traditional arrangement that requires a dedicated installation and that is completely independent and separated from the rolling, drawings or extrusion devices that are usually upstream or downstream disposed.
Purpose of the present invention is to achieve a device, and perfect a relative method, for the in-line detection of surface defects in a rolled product which allows a highly sensitive detection of the defects, in continuous rolling lines, and which reduces the times needed for configuration and re-equipping compared with known systems.
The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.